Disclosure of Invention
In view of the above, the invention provides a pile foundation load influence assessment method, medium and system by pile sinking soil compaction effect, which can solve the technical problems that monitoring data and theoretical analysis results are difficult to effectively fuse in the prior art, so that the reliability and pertinence of the assessment results are weaker, and sufficient basis is difficult to provide for engineering design.
The invention is realized in the following way:
The first aspect of the invention provides a method for evaluating the impact of a pile sinking soil compaction effect on pile foundation load, which comprises the following steps:
S10, installing a plurality of vibration sensors and strain sensors at different depths and distances around a pile foundation, and continuously collecting vibration signals and strain signals in the downward construction process of the pile foundation to form a vibration-strain signal group;
s20, preprocessing the acquired vibration-strain signals, including denoising, filtering and signal alignment, so as to improve the data quality;
S30, determining the optimal time window length by adopting a time-frequency analysis method according to each signal in the aligned vibration-strain signal group so as to capture the characteristics of vibration and deformation of soil around the pile foundation;
S40, extracting time-frequency characteristics of each signal, including amplitude, frequency, phase and strain, by using the determined optimal time window length, and marking the time-frequency characteristics of all signals as a characteristic group to be detected;
S50, establishing a kinetic equation set, including a soil body kinetic equation, a soil body stress-strain relation equation, a soil body vibration propagation equation, a soil body deformation coordination equation and a pile-soil interaction equation;
S60, solving the kinetic equation set to obtain a plurality of analytic solutions, wherein the analytic solutions are respectively a first analytic solution for describing vibration propagation characteristics of soil bodies around the pile foundation, a second analytic solution for describing stress distribution characteristics of the soil bodies around the pile foundation, a third analytic solution for describing deformation characteristics of the soil bodies around the pile foundation, a fourth analytic solution for describing interaction characteristics of pile and soil and a fifth analytic solution for describing bearing capacity characteristics of the pile foundation;
S70, establishing a pile sinking soil squeezing effect mathematical model according to the plurality of analytic solutions and initial conditions and boundary conditions of the dynamic equation set, and solving the stress-strain state of the soil around the pile by taking the feature set to be detected as an input parameter;
S80, calculating the change of the side friction resistance and the end resistance of the pile foundation based on the solved stress-strain state of the soil body around the pile, and further evaluating the influence of the soil squeezing effect on the bearing capacity of the pile foundation as an evaluation result;
And S90, calculating the overall bearing capacity change index of the pile foundation according to the evaluation result, determining the influence degree of the soil squeezing effect on the pile foundation load, and marking a potential bearing capacity reduction area.
The step S10 specifically comprises the steps of installing a plurality of vibration sensors and strain sensors at different depths and distances around the pile foundation. The sensors are used for continuously collecting vibration signals and strain signals in the pile foundation construction process. The vibration sensor is mainly used for capturing the vibration characteristics of surrounding soil, and the strain sensor is used for monitoring the strain change of the soil. The sensors should be arranged at different positions and depths around the pile foundation to comprehensively acquire the space-time distribution characteristics of soil vibration and deformation. By reasonably arranging the sensor array, the complete information of the soil dynamic response in the pile foundation construction process can be effectively recorded, and basic data is provided for subsequent analysis and evaluation.
The step S20 specifically includes preprocessing the collected vibration-strain signal, including denoising, filtering, signal alignment and the like. Firstly, denoising is needed to be carried out on an original signal so as to eliminate the influence of external interference noise on the signal. Common denoising methods include wavelet denoising, adaptive filtering, and the like. And secondly, filtering the signals, namely, reserving frequency bands related to soil vibration and deformation by adopting a band-pass filter, and removing irrelevant high and low frequency components. Finally, the signals acquired by the different sensors need to be time aligned to eliminate time misalignment due to propagation delay or acquisition time differences. The pretreatment measures can effectively improve the quality and reliability of signals, and lay a foundation for subsequent time-frequency analysis.
The step S30 specifically includes determining an optimal time window length by using a time-frequency analysis method according to the aligned vibration-strain signal group. Time-frequency analysis is a very effective signal analysis tool, and can reflect the characteristics of signals in the time domain and the frequency domain at the same time. In the invention, the purpose of the time-frequency analysis is to capture the time-varying characteristics of the vibration and deformation of the soil surrounding the pile foundation. By performing short-time Fourier transform or wavelet transform on each sensor signal, a time-frequency characteristic spectrum of the signal can be obtained. And then, combining the physical processes of soil vibration and deformation, and determining the optimal time window length capable of fully reflecting the response characteristics of the soil. The time window length determines the time resolution of the subsequent time-frequency feature extraction and is important for accurately describing the soil dynamic response.
The step S40 specifically includes extracting time-frequency characteristics of each signal, including amplitude, frequency, phase, strain, and the like, by using the optimal time window length determined in the step S30. Specifically, short-time Fourier transform is performed on each sensor signal to obtain a time-frequency characteristic spectrum of the sensor signal. Characteristic parameters such as amplitude, frequency and phase are extracted from the atlas, and the vibration states of the soil body at different time frequency points are described. Meanwhile, the deformation characteristics of the soil body can be directly obtained by utilizing the strain signals measured by the sensor. And (3) sorting the time-frequency characteristic parameters of all the sensor signals into a characteristic parameter set to be used as input data for subsequent analysis. The time-frequency characteristic parameters can comprehensively describe the dynamic response process of soil around the pile foundation, and are the basis for building the soil-pile interaction model.
The step S50 specifically comprises the step of establishing an equation set for describing pile foundation-soil body dynamics behavior, wherein the equation set comprises a soil body dynamics equation, a soil body stress-strain relation equation, a soil body vibration propagation equation, a soil body deformation coordination equation, a pile-soil interaction equation and the like. The equations together form a complete equation set for describing the dynamics behavior of the pile foundation and the soil body, and a foundation is laid for subsequent analysis and solution.
The step S60 specifically includes solving the equation set established in the step S50 to obtain a plurality of analytical solutions, wherein the vibration propagation characteristics, the stress distribution characteristics, the deformation characteristics, the pile-soil interaction characteristics and the pile foundation bearing capacity characteristics of soil around the pile foundation are respectively described. The analysis solutions comprehensively reflect all aspects and features of the pile foundation-soil body power system, and provide a foundation for the establishment of a subsequent mathematical model.
The step S70 specifically includes establishing a mathematical model of pile sinking soil squeezing effect according to the plurality of analytical solutions obtained in the step S60, and initial conditions and boundary conditions of the equation set. Substituting the feature set to be measured obtained in the step S40 into the analysis solution as an input parameter, and solving the stress-strain state of the soil body around the pile by a numerical calculation mode. The core of the mathematical model is to simulate and predict the stress-strain response characteristics of surrounding soil in the pile foundation construction process by utilizing the time-frequency characteristics of vibration-strain signals and solving a kinetic equation set.
The step S80 specifically comprises the step of calculating the change conditions of the side friction resistance and the end resistance of the pile foundation based on the stress-strain state of the soil body around the pile obtained in the step S70. Firstly, calculating shear strength parameters of soil around the pile foundation by utilizing the soil strain state, and further calculating the side friction resistance according to a classical formula. And secondly, calculating the bearing area and stress distribution of the pile foundation end by using the soil stress state, and further calculating the end resistance. And finally, taking the calculated change conditions of the side friction resistance and the end resistance as evaluation results, and reflecting the influence of the pile sinking soil squeezing effect on the total bearing capacity of the pile foundation.
The step S90 specifically includes calculating an overall bearing capacity change index of the pile foundation according to the pile foundation bearing capacity change evaluation result obtained in the step S80. The index reflects the degree of influence of the soil squeezing effect on the pile foundation bearing capacity. By analyzing the value of the index, the influence degree of the soil squeezing effect on pile foundation load can be determined. Meanwhile, a potential bearing capacity reduction area needs to be marked according to the stress-strain distribution situation of the soil body around the pile, which is obtained in the step S70. The information is helpful to take reinforcing measures in a targeted manner, and ensures that the pile foundation still can meet the design requirements under the action of soil squeezing effect.
Wherein, the soil mass dynamics equation is specifically:
The soil mass dynamics equation is specifically as follows:
wherein ρ is soil density in kg/m3, u is soil displacement vector in m, t is time in s; the method is a divergence operator, sigma is a stress tensor, the unit is Pa, and B is a physical strength vector of unit mass, and the unit is N/kg.
The soil stress-strain relation equation is specifically as follows:
σ=D·∈;
wherein sigma is stress tensor, the unit is Pa, d is rigidity matrix, the unit is Pa, and E is strain tensor, and the method is dimensionless.
Wherein, soil mass vibration propagation equation specifically is:
Wherein u is soil displacement vector, the unit is m, t is time, the unit is s, c is wave propagation speed, and the unit is m/s; Is a laplace operator.
Wherein, the soil deformation coordination equation specifically is:
Wherein, pile soil interaction equation specifically is:
p=C1·Es·u+C2·σ′v·tanφ·u;
wherein p is the interaction force of pile-soil interface, the unit is N/m2, u is the displacement vector of soil, the unit is m, C1 and C2 are empirical coefficients, Es is the elastic modulus of soil, sigma'v is effective vertical stress, and phi is internal friction angle.
Wherein the plurality of analytical solutions are respectively:
the first analytic solution describes the vibration propagation characteristics of the soil body around the pile foundation, namely the propagation rule of vibration signals in the soil body in time and space, and is specifically expressed as follows:
u(x,T)=A cos(ωt-kx);
Wherein A is amplitude, ω is angular frequency, and k is wave number;
The second analytic solution describes the stress distribution characteristics of the soil body around the pile foundation, namely the stress state of the soil body in the pile foundation construction process, and is specifically expressed as follows:
σ(x,t)=B exp(-αxc)sin(ωt-kx+φ);
wherein B is stress amplitude, alpha is attenuation coefficient, and phi is phase;
the third analytic solution describes the deformation characteristics of the soil body around the pile foundation, namely the displacement and strain state of the soil body in the pile foundation construction process, and is specifically expressed as follows:
∈(x,t)=C exp(-βx)cos(ωt-KX+θ);
wherein C is the strain amplitude, beta is the attenuation coefficient, and theta is the phase;
The fourth analytical solution describes the characteristics of pile-soil interaction, namely the interaction force between the pile foundation and the surrounding soil mass, and is specifically expressed as:
p(x,t)=Dexp(-γx)sin(ωt-kx+ψ);
Wherein D is the amplitude of the interaction force, gamma is the attenuation coefficient, and ψ is the phase;
The fifth analytic solution describes the characteristics of pile foundation bearing capacity, namely the bearing capacity change of the pile foundation under the action of soil squeezing effect, and is specifically expressed as:
In the formula,For the bearing capacity of the pile foundation before construction, deltaQ (t) is the time-varying bearing capacity change rate.
Wherein, the whole bearing capacity change index of pile foundation specifically is:
In the formula,AndThe total bearing capacity of pile foundations before and after construction is respectively.
Optionally, the sensor mounting positions in the step S10 include different depth positions such as a top, a middle and a bottom of the pile foundation, and different radial distances around the pile foundation. Thus, vibration and deformation response information of the soil body at different positions and depths can be comprehensively obtained.
Optionally, the preprocessing in step S20 further includes normalizing the signals to eliminate dimensional effects caused by sensor installation locations, parameter differences, and the like.
Optionally, the time-frequency analysis method in step S30 may also use other time-frequency analysis techniques such as wavelet packet analysis. The methods can effectively extract time-frequency characteristics and lay a foundation for subsequent modeling analysis.
Optionally, the time-frequency characteristic in step S40 further includes parameters such as a power spectral density, a coherence function, and the like. These parameters may further reflect the energy characteristics and correlation of the vibration and deformation of the soil mass.
Optionally, the mathematical model in step S70 may be further solved by using a numerical simulation method such as finite element or boundary element, so as to improve accuracy and stability of calculation.
Optionally, when calculating the side friction resistance in step S80, a reasonable intensity distribution model is established by considering the law of the change of the soil intensity with the depth.
A second aspect of the present invention provides a computer readable storage medium, where the computer readable storage medium stores program instructions, where the program instructions are executed to perform a pile foundation load impact assessment method according to the above-mentioned pile driving soil compaction effect.
A third aspect of the present invention provides a pile foundation load impact assessment system by using pile driving soil squeezing effect, wherein the pile foundation load impact assessment system comprises the computer readable storage medium.
Compared with the prior art, the pile foundation load influence assessment method, medium and system by the pile sinking soil squeezing effect provided by the invention have the beneficial effects that:
1. The method has the advantages that the on-site monitoring data are fully utilized, a plurality of vibration sensors and strain sensors are distributed around the pile foundation, vibration and deformation response information of the soil body in time and space can be continuously collected, and comprehensive basic data are provided for subsequent analysis. Compared with the existing method which only relies on single-point monitoring, the method can capture the dynamic response characteristics of soil around the pile foundation more accurately.
2. The method can extract time-frequency characteristic parameters of vibration-strain signals, such as amplitude, frequency, phase and the like, by using time-frequency analysis means, such as short-time Fourier transform, wavelet transform and the like. The time-frequency characteristics can describe the vibration and deformation process of the soil body more comprehensively, and a good foundation is laid for subsequent modeling analysis.
3. The method establishes a complete equation set comprising a soil dynamics equation, a constitutive equation, a vibration propagation equation and the like on the basis of acquiring the soil dynamic response characteristics, and can accurately simulate and predict the stress-strain state of surrounding soil in the pile foundation construction process by solving the equations through numerical values. The modeling method based on dynamic analysis is more practical than the existing static or quasi-static analysis.
In general, the pile sinking soil compaction effect evaluation method based on vibration-strain signal analysis fully fuses field monitoring data and dynamics theory analysis, can evaluate the change condition of pile foundation bearing capacity more accurately and comprehensively, and solves the technical problems that monitoring data and theory analysis results in the prior art are difficult to fuse effectively, so that the reliability and pertinence of evaluation results are weaker, and sufficient basis is difficult to provide for engineering design.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
As shown in fig. 1, the invention provides a method for evaluating pile foundation load influence by pile sinking soil compaction effect, which comprises the following steps:
S10, installing a plurality of vibration sensors and strain sensors at different depths and distances around a pile foundation, and continuously collecting vibration signals and strain signals in the downward construction process of the pile foundation to form a vibration-strain signal group;
s20, preprocessing the acquired vibration-strain signals, including denoising, filtering and signal alignment, so as to improve the data quality;
S30, determining the optimal time window length by adopting a time-frequency analysis method according to each signal in the aligned vibration-strain signal group so as to capture the characteristics of vibration and deformation of soil around the pile foundation;
S40, extracting time-frequency characteristics of each signal, including amplitude, frequency, phase and strain, by using the determined optimal time window length, and marking the time-frequency characteristics of all signals as a characteristic group to be detected;
S50, establishing a kinetic equation set, including a soil body kinetic equation, a soil body stress-strain relation equation, a soil body vibration propagation equation, a soil body deformation coordination equation and a pile-soil interaction equation;
S60, solving a kinetic equation set to obtain a plurality of analytic solutions, wherein the analytic solutions are respectively a first analytic solution for describing vibration propagation characteristics of soil bodies around a pile foundation, a second analytic solution for describing stress distribution characteristics of the soil bodies around the pile foundation, a third analytic solution for describing deformation characteristics of the soil bodies around the pile foundation, a fourth analytic solution for describing interaction characteristics of pile and soil and a fifth analytic solution for describing bearing capacity characteristics of the pile foundation;
S70, establishing a pile sinking soil squeezing effect mathematical model according to a plurality of analytic solutions and initial conditions and boundary conditions of a dynamic equation set, and solving the stress-strain state of the soil body around the pile by taking the feature set to be tested as an input parameter;
S80, calculating the change of the side friction resistance and the end resistance of the pile foundation based on the solved stress-strain state of the soil body around the pile, and further evaluating the influence of the soil squeezing effect on the bearing capacity of the pile foundation as an evaluation result;
And S90, calculating the overall bearing capacity change index of the pile foundation according to the evaluation result, determining the influence degree of the soil squeezing effect on the pile foundation load, and marking a potential bearing capacity reduction area.
The following describes in detail the specific embodiments of the above steps:
In step S10, a plurality of vibration sensors and strain sensors are installed at different depths and distances around the pile foundation for continuously collecting vibration signals and strain signals during the construction of the pile foundation.
For the vibration signal, an acceleration sensor may be used to measure the vibration acceleration a (x, t) of the soil mass, where x represents the position coordinates of the sensor in the horizontal direction and t represents the time coordinates. According to Newton's second law, the following relationship exists between the vibration acceleration and the dynamic response force fd (x, t) of the soil mass:
Wherein ρ is the soil density and V is the soil volume.
For strain signals, strain gages may be used to measure the strain ε (x, t) of the soil mass. The strain and the displacement u (x, t) of the soil body have the following relation:
By reasonably arranging the sensor array, the space-time distribution information of the soil body around the pile foundation in vibration and deformation can be obtained, and basic data are provided for subsequent analysis and evaluation.
In step S20, the collected vibration-strain signal needs to be preprocessed, including denoising, filtering, signal alignment, and the like.
First, the original signal needs to be subjected to denoising processing. One common approach is wavelet denoising, which uses wavelet transforms to decompose a signal and remove high frequency noise components. The wavelet transform is expressed as:
Wherein, psia,b (t) is a wavelet basis function with a scale of a and a translation of b, and W (a, b) is a wavelet coefficient. By setting a proper threshold, noise components can be effectively removed, and the signal quality is improved.
Second, a filtering process is required for the signal. One common approach is a band pass filter that preserves the frequency band associated with soil vibration and deformation, removing extraneous high and low frequency components. The transfer function of a bandpass filter can be expressed as:
where ωc is the cut-off frequency and n is the filter order. By adjusting the filter parameters, the desired band characteristics can be obtained.
Finally, the signals acquired by the different sensors need to be time aligned. This can be achieved by means of time delay compensation, i.e. by performing the following time shift operations on each signal:
fa(t)＝f(t-τa)
Where fa (t) is the aligned signal and τa is the time delay. By determining the optimal delay τa, time misalignments due to propagation delays or acquisition time differences can be eliminated.
Through the pretreatment measures, the quality and the reliability of signals can be effectively improved, and a foundation is laid for subsequent time-frequency analysis.
In step S30, an optimal time window length is determined by using a time-frequency analysis method according to the aligned vibration-strain signal group. Time-frequency analysis is a very effective signal analysis tool that can reflect the characteristics of a signal in both the time and frequency domains.
One common time-frequency analysis method is the short-time fourier transform (STFT), which can be expressed as:
Where f (t) is the signal to be analyzed and w (t) is the window function. The STFT can obtain the energy distribution of the signals on a time-frequency plane, so that the time-varying characteristics of soil vibration and deformation are reflected.
By performing an STFT operation on each sensor signal, a time-frequency characteristic spectrum thereof can be obtained. Combining the physical processes of soil vibration and deformation, the optimal time window length Tw capable of fully reflecting the response characteristics of the soil needs to be determined. The time window length determines the time resolution of the subsequent time-frequency feature extraction and is important for accurately describing the soil dynamic response.
In step S40, the time-frequency characteristics of each signal, including amplitude, frequency, phase, strain magnitude, and the like, are extracted using the optimal time window length Tw determined in step S30.
For the vibration signal, the following time-frequency characteristic parameters can be extracted:
A(t,ω)=|STFT(t,v)|
φ(t,ω)=∠STFT(t,ω)
Where a (t, ω) represents the amplitude of the signal in the time-frequency plane, ω (t) represents the instantaneous frequency of the signal, and Φ (t, ω) represents the instantaneous phase of the signal. The parameters can comprehensively describe the vibration states of the soil body at different time frequency points.
For strain signals, direct extraction can be performed:
ε(x,t)
The time-frequency characteristic parameters of all sensor signals are arranged into a characteristic parameter set X= { A, omega, phi, epsilon }, and the characteristic parameter set X= { A, omega, phi, epsilon } is used as input data for subsequent analysis.
In step S50, a system of equations describing the dynamics of pile foundation-soil mass is established, comprising the following equations:
1. Soil mass dynamics equation:
wherein ρ is soil density, u is soil displacement, σ is soil stress tensor, and b is physical strength. The equation describes the equation of motion of the soil mass.
2. Soil stress-strain relation equation:
σ=D·∈
Wherein D is the rigidity matrix of the soil body, and E is the strain tensor of the soil body. The equation characterizes constitutive relation of soil.
3. Soil mass vibration propagation equation:
Where c is the wave propagation velocity of the soil mass. The equation describes the propagation characteristics of the vibration signal in the soil.
4. A soil deformation coordination equation:
The equation indicates that the soil deformation needs to meet the continuity condition.
5. Pile-soil interaction equation:
p=f(u,∈)
Wherein p is the interaction force of pile foundation-soil body interface. The equation describes the interaction between the pile foundation and the surrounding soil mass.
The equations together form a complete equation set for describing the dynamics behavior of the pile foundation and the soil body, and a foundation is laid for subsequent analysis and solution.
In step S60, the equation set established in step S50 is solved to obtain a plurality of analytical solutions.
1. First analytical solution:
The analytical solution describes the vibration propagation characteristics of the soil body around the pile foundation, namely the propagation rule of vibration signals in the soil body in time and space. Can be expressed as:
u(x,t)=A cos(ωt-kx)
Where A is amplitude, ω is angular frequency, and k is wavenumber. The analytical solution reflects the propagation characteristics of the fluctuation signals in the soil body and provides a basis for evaluating the vibration influence around the pile foundation.
2. Second analytical solution:
the analysis solution describes the stress distribution characteristics of the soil body around the pile foundation, namely the stress state of the soil body in the pile foundation construction process. Can be expressed as:
σ(x,t)=B exp(-αx)sin(ωt-kx+φ)
Wherein B is stress amplitude, alpha is attenuation coefficient, and phi is phase. The analysis solution reflects the change rule of soil stress along with space and time, and provides a basis for evaluating the soil stress state around the pile foundation.
3. Third analytical solution:
the analytic solution describes the deformation characteristics of the soil body around the pile foundation, namely the displacement and strain state of the soil body in the pile foundation construction process. Can be expressed as:
∈(x,t)=C exp(-βx)cos(ωt-kx+θ)
Wherein C is the strain amplitude, beta is the attenuation coefficient, and theta is the phase. The analysis solution reflects the change rule of soil deformation along with space and time, and provides a basis for evaluating the deformation state of soil around the pile foundation.
4. Fourth analytical solution:
The analytical solution describes the characteristics of pile-soil interaction, i.e. the interaction forces between pile foundation and surrounding soil. Can be expressed as:
p(x,t)=Dexp(-γx)sin(ωt-kx+ψ)
Where D is the magnitude of the interaction force, γ is the attenuation coefficient, and ψ is the phase. The analysis solution reflects the dynamic interaction characteristics between the pile foundation and the soil body, and provides a basis for analyzing the stress state of the pile foundation.
5. Fifth analytical solution:
the analysis solution describes the characteristics of the bearing capacity of the pile foundation, namely the bearing capacity change of the pile foundation under the action of the soil squeezing effect. Can be expressed as:
wherein,For the bearing capacity of the pile foundation before construction, deltaQ (t) is the time-varying bearing capacity change rate. This analytical solution provides the basis for subsequent load bearing assessment.
The analysis solutions comprehensively reflect all aspects and features of the pile foundation-soil body power system, and provide a foundation for the establishment of a subsequent mathematical model.
In step S70, a mathematical model of the pile-driving effect is built based on the plurality of analytical solutions obtained in step S60, and the initial conditions and boundary conditions of the equation set.
And substituting the characteristic parameter set X to be detected obtained in the step S40 into the analysis solution, and solving the stress-strain state of the soil body around the pile by a numerical calculation mode.
Specifically, the following mathematical model may be constructed:
wherein,To the point ofThe mapping relations of soil displacement, stress, strain, pile-soil interaction force and pile foundation bearing capacity obtained by the analysis and solution in the step S60 are respectively shown. By numerically solving the equations, the stress-strain state of the soil body around the pile can be obtained, and a foundation is provided for subsequent bearing capacity evaluation.
The core of the mathematical model is to simulate and predict the stress-strain response characteristics of surrounding soil in the pile foundation construction process by utilizing the time-frequency characteristics of vibration-strain signals and solving a kinetic equation set. The model comprises a plurality of aspects of soil vibration propagation, stress distribution, deformation characteristics, pile-soil interaction and the like, and can accurately reflect the disturbance process of pile foundation construction on surrounding soil.
In step S80, the change conditions of the side friction resistance and the end resistance of the pile foundation are calculated based on the pile periphery soil stress-strain state obtained in step S70.
Firstly, calculating shear strength parameters of soil around the pile foundation, such as cohesion c and internal friction angle phi, by utilizing the soil strain state epsilon, and further according to classical Mohr-Coulomb strength criterion:
τ=c+σntanφ
The side friction resistance Qs was calculated. Wherein σn is the normal stress.
Secondly, calculating the bearing area Ab and the stress distribution sigmab of the pile foundation end by using the soil body stress state sigma, and further according to the formula:
Qb＝σbAb
end resistance Qb is calculated.
And finally, taking the calculated change conditions of the side friction resistance and the end resistance as evaluation results, and reflecting the influence of the pile sinking soil squeezing effect on the total bearing capacity of the pile foundation.
The key of the step is to accurately capture the change rule of the stress-strain state of the soil body around the pile foundation, so as to reasonably calculate the change of the bearing capacity of the pile foundation. The obtained evaluation result provides basis for the next impact analysis.
In step S90, the overall bearing capacity change index η of the pile foundation is calculated based on the pile foundation bearing capacity change evaluation result obtained in step S80. The index reflects the influence degree of soil squeezing effect on pile foundation bearing capacity, and can be expressed as:
In the formula,AndThe total bearing capacity of pile foundations before and after construction is respectively.
By analyzing the value of eta, the influence degree of the soil squeezing effect on pile foundation load can be determined. If eta is less than-5%, the soil squeezing effect causes a larger degree of bearing capacity reduction, and importance needs to be attached, if eta is between-5% and +5%, the impact of the soil squeezing effect on the bearing capacity is smaller and acceptable, and if eta is greater than +5%, the soil squeezing effect has a certain degree of enhancement on the bearing capacity.
Meanwhile, the potential bearing capacity reduction area is marked according to the stress-strain distribution conditions of the soil body around the pile, sigma (x, t) and epsilon (x, t) obtained in the step S70. Certain stress or strain thresholds σc and εc can be set and when the stress or strain of a localized area exceeds these thresholds, it is considered a potential load-bearing capacity-reducing area, requiring significant attention. The information is helpful to take reinforcing measures in a targeted manner, and ensures that the pile foundation still can meet the design requirements under the action of soil squeezing effect.
The thresholds σc and εc may be determined from engineering experience and related specifications, for example:
σc＝0.8σy
∈c=0.01
Wherein sigmay is the yield stress of the soil body.
In general, the method provided by the invention can comprehensively evaluate the influence of the pile sinking soil compaction effect on the bearing capacity, and provides an important reference basis for pile foundation design and construction. The whole method relates to a plurality of disciplinary fields, such as soil mechanics, structural dynamics, signal processing and the like, and has strong academic and innovative performances.
Through the detailed description of the steps S10-S90, it can be seen that the method fully utilizes the time-frequency characteristics of the vibration-strain signals, and simulates and predicts the stress-strain response of surrounding soil in the pile foundation construction process by establishing a pile foundation-soil dynamics model, so as to evaluate the influence of the soil squeezing effect on the bearing capacity of the pile foundation. The method based on the combination of the monitoring data and the mechanical analysis not only can quantitatively describe the soil squeezing effect, but also has stronger pertinence and operability for engineering application.
The sources or acquisitions of the relevant variables are provided below as a) ρ (soil mass density) sources obtained by field or laboratory tests. The acquisition mode can be a field test method such as a cutting ring method, a sand filling method and the like, or calculated by mass-volume ratio in a laboratory.
B) u (soil displacement) is obtained by on-site monitoring. The acquisition mode can be to use displacement sensor, inclinometer and other instruments to measure.
C) Sigma (soil stress tensor) source, obtained by field test or theoretical calculation. The acquisition mode can be that an instrument such as a soil pressure box can be used for measurement or calculation is carried out through a stress analysis method.
D) D (soil rigidity matrix) is obtained through laboratory test or empirical formula. The acquisition mode is that the elastic modulus and the poisson ratio of the soil body can be determined through a triaxial test, a shear test and the like, so that a rigidity matrix is constructed.
E) E (soil strain tensor) sources obtained by on-site monitoring or theoretical calculation. The acquisition mode can be that an instrument such as a strain gauge is used for measurement or displacement gradient calculation is carried out.
F) c (wave propagation velocity) source, obtained by field test or empirical formula. The acquisition mode is that the wave velocity tester can be used for carrying out field test or estimating by adopting an empirical formula according to the soil type and the physical property.
G) p (pile-soil interface interaction force) is obtained by field test or theoretical model. The acquisition mode can be that instruments such as pile side friction resistance meters and the like are used for measurement or the pile-soil interaction model is used for calculation.
H) A, B, C, D (amplitude parameters) are derived from signal analysis. The acquisition mode is that the acquired vibration-strain signals are subjected to time-frequency analysis, and corresponding amplitude parameters are extracted.
I) Omega (angular frequency), k (wave number), alpha, beta, gamma (attenuation coefficient), phi, theta, phi (phase) sources obtained by signal analysis and wave theory. The acquisition mode is that the acquired signals are subjected to time-frequency analysis, and the parameters are determined by combining the fluctuation propagation theory.
J) Qb (pile foundation bearing capacity) is obtained by field test or theoretical calculation. The acquisition mode can be directly measured through static load test or theoretical calculation is carried out according to soil parameters and pile foundation parameters.
K) c (cohesion) and phi (internal friction angle) from laboratory tests or field tests. The acquisition mode can be determined by laboratory methods such as triaxial test and direct shear test, or on-site shear test.
L) σn (normal stress) source, obtained by field test or theoretical calculation. The acquisition mode can be measured by using a soil pressure cell or calculated by a stress analysis method.
M) Ab (pile foundation end bearing area) is determined according to pile foundation design parameters. The acquisition mode is direct measurement or calculation according to the design drawing of the pile foundation.
N) sigmab (pile tip stress distribution) obtained by field test or theoretical calculation. The acquisition mode can be measured by using a pile tip stress meter or calculated by a stress transmission theory.
Accurate acquisition of these variables is critical to assessing the impact of pile-driving effects. In practical applications, it may be necessary to combine various test methods and theoretical analysis to determine these parameters to ensure reliability of the evaluation results.
It should be noted that, the functional relationship f in the pile-soil interaction equation p=f (u, e) is a complex problem, and the acquisition method involves multiple aspects of theoretical analysis, experimental study, numerical simulation and the like. I will explain in detail several main ways to get this functional relationship:
1. theoretical model:
the theoretical model establishes a mathematical expression of pile-soil interaction through mechanical analysis. Common theoretical models include:
a) Elastic Winkler model:
p=khu
Where kh is the horizontal foundation reaction coefficient.
B) p-y curve method:
Where pu is the limiting lateral earth pressure, A is the empirical coefficient and y is the horizontal displacement.
Parameters of these theoretical models can be obtained through geotechnical tests or empirical formulas.
2. Field test:
and the pile-soil interaction relationship is directly measured through field test. The main method comprises the following steps:
a) And (3) horizontal load test, namely carrying out horizontal load test on the single pile, and measuring the horizontal displacement and the corresponding soil pressure of the pile.
B) And (3) power pile testing, namely analyzing the power response of the pile by a power pile testing method, and inverting pile-soil interaction parameters.
C) And (3) testing a centrifugal machine, namely simulating actual engineering conditions in the centrifugal machine and measuring the pile-soil interaction relationship.
3. Indoor model test:
small-sized model experiments were performed in the laboratory to study the pile-soil interaction mechanism. The common methods include:
a) And (3) carrying out a shear box test, namely simulating the shear characteristics of the pile soil interface.
B) And (3) a ring shear test, namely researching the large deformation characteristic of the pile soil interface.
C) And (3) a pressure chamber test, namely researching pile-soil interaction under a controllable stress condition.
4. Numerical simulation:
and simulating pile-soil interaction process by using numerical methods such as finite elements, finite differences and the like. The method mainly comprises the following steps:
a) And establishing a soil body constitutive model, such as a Mohr-Coulomb model, a Drucker-Prager model and the like.
B) Simulating pile-soil contact surface, such as by using contact units or interface elements.
C) And carrying out parameterization research to obtain pile-soil interaction relations under different conditions.
5. The artificial intelligence method comprises the following steps:
and training a pile-soil interaction model based on a large amount of measured data by using a machine learning algorithm. The method comprises the following steps:
a) And constructing a multi-layer neural network, inputting soil parameters and geometric parameters of piles, and outputting interaction force.
B) And a support vector machine, which is to establish a nonlinear mapping relation of pile-soil interaction based on the existing data.
C) And (3) optimizing parameters of the pile-soil interaction model by a genetic algorithm.
6. Semi-empirical method:
And combining theoretical analysis and engineering experience to provide a semi-empirical formula. Such as:
p=C1·Es·u+C2·σ′v·tanφ·u
Wherein C1 and C2 are experience coefficients, Es is soil body elastic modulus, sigma'v is effective vertical stress, and phi is internal friction angle.
In practical applications, it is generally necessary to comprehensively use a plurality of methods to obtain the pile-soil interaction functional relationship:
1. First, a preliminary functional form is built based on a theoretical model.
2. Then, the key parameters are obtained through field test or indoor test.
3. And carrying out parameterization research by using a numerical simulation method, and expanding the application range of the function.
4. If there is sufficient data, optimization of the model using machine learning methods can be considered.
5. And finally, correcting and calibrating the model by combining engineering experience.
It should be noted that the pile-soil interaction relationship is affected by various factors, such as soil type, stress state, pile geometry, etc. Thus, the functional relationship obtained should be specific to the particular engineering conditions and should be noted for its scope of application when in use. In actual engineering, field verification and adjustment may be required to ensure accuracy and reliability of the model.
A second aspect of the present invention provides a computer readable storage medium, where the computer readable storage medium stores program instructions, where the program instructions are executed to perform a pile foundation load impact assessment method according to the above-mentioned pile driving soil compaction effect.
A third aspect of the present invention provides a pile foundation load impact assessment system by using pile driving soil squeezing effect, wherein the pile foundation load impact assessment system comprises the computer readable storage medium.
Specifically, the principle of the invention is as follows:
1. And the dynamic response of soil is comprehensively described by utilizing the multipoint dynamic monitoring data, namely, the surrounding soil can generate complex vibration and deformation response in the pile foundation construction process. According to the method, the plurality of vibration sensors and the strain sensors are distributed around the pile foundation, so that dynamic response signals of soil in time and space can be continuously collected. Compared with the existing single-point or small-amount monitoring data, the multipoint monitoring mode can capture the space-time distribution characteristics of the soil body dynamic response more comprehensively, and lays a more reliable foundation for subsequent analysis.
2. By adopting a time-frequency analysis technology, characteristic parameters are extracted to describe soil body response, namely the dynamic response of the soil body often has obvious time-varying characteristics, and the dynamic characteristics of the soil body are difficult to fully reflect only by virtue of time-domain analysis. The method of the invention utilizes time-frequency analysis technology, such as short-time Fourier transform and wavelet transform, to extract the characteristic parameters of amplitude, frequency, phase and the like from the vibration-strain signal, and the parameters can more comprehensively describe the vibration and deformation characteristics of the soil body on the time-frequency domain.
3. The method establishes a complete equation set for describing the dynamics behavior of the pile foundation and the soil body on the basis of obtaining time-frequency characteristic parameters, and comprises a soil body dynamics equation, a stress-strain relation equation, a vibration propagation equation and the like. By solving the equations, the stress-strain distribution condition of soil around the pile foundation can be obtained, and a basis is provided for subsequent bearing capacity evaluation. Compared with the existing static or quasi-static analysis, the modeling method based on the dynamic analysis is more in line with the actual engineering situation.
For better understanding and implementation of the present invention, one of the specific application scenarios of the present invention is provided below as an example, where a high-rise building engineering is located in a coastal area, and the foundation is a reinforced concrete pile foundation. Because of complex geological conditions, a more serious pile sinking soil squeezing effect can occur in the construction process, and a certain influence is generated on the bearing capacity of the pile foundation. In order to evaluate the influence of soil squeezing effect on engineering safety, a construction unit decides to adopt the pile foundation bearing capacity evaluation method based on vibration-strain signal analysis provided by the invention to monitor and analyze the engineering in detail.
1. In-situ monitoring installation
According to the requirements of the method, 12 vibration sensors and 12 strain sensors are installed at different depths and distances around the pile foundation. The specific arrangement is as follows:
The vibration sensor is arranged in such a way that 4 sensors are respectively arranged at the top (2 m) of the pile foundation, the middle (10 m) of the pile foundation and the bottom (20 m) of the pile foundation, and are respectively positioned at the positions of 1m, 2m, 3m and 4m of the horizontal distance around the pile foundation.
And the strain sensor is arranged in a way that the arrangement positions of the strain sensor are consistent with that of the vibration sensor, 4 sensors are respectively arranged at the top, the middle and the bottom of the pile foundation, and the horizontal distances are respectively 1m, 2m, 3m and 4m.
According to the sensor arrangement scheme, vibration and strain response information of soil around the pile foundation at different depths and positions can be fully obtained, and a foundation is laid for subsequent analysis and evaluation.
2. Signal preprocessing
The vibration acceleration signal a (x, t) and the strain signal epsilon (x, t) acquired on site are preprocessed, and the preprocessing comprises denoising, filtering, time alignment and other operations.
First, wavelet denoising processing is performed on an original signal. And selecting Daubechies 4-order wavelet basis function, decomposing by 5 layers of wavelets, and filtering out high-frequency components to obtain a denoised signal. This step can effectively remove the influence of external vibration noise on the measurement data.
And secondly, carrying out band-pass filtering on the denoised signal. The cut-off frequency of the filter is set to be 1Hz and 100Hz, so that the main frequency band related to soil vibration and deformation can be reserved, and irrelevant high and low frequency components can be removed.
Finally, the signals acquired by the different sensors are time aligned. The optimal time delay τa of each signal relative to the reference signal is determined by correlation analysis and corrected. This eliminates time misalignments due to propagation delays or acquisition time differences.
Through the pretreatment, high-quality vibration-strain signal data are obtained, and a foundation is laid for subsequent time-frequency analysis.
3. Time-frequency feature extraction
According to step S30, a time-frequency analysis is performed on the preprocessed signal using a short-time fourier transform (STFT), and an optimal time window length Tw is determined. Through analysis, the optimal time window length Tw =0.5 s is determined, so that the transient characteristic of the soil vibration response can be captured well.
Next, using the determined Tw, the time-frequency characteristic parameters of the vibration-strain signal of each monitoring point are extracted, including the amplitude a (T, ω), the frequency ω (T), the phase Φ (T, ω), the strain ε (x, T), and the like. These time-frequency characteristic parameters constitute a characteristic parameter set X, which provides input for a subsequent analytical model.
4. Kinetic analysis model establishment
According to step S50, a complete equation set describing the pile foundation-soil body dynamics behavior is established, including:
(1) Soil mass dynamics equation:
(2) Soil constitutive relation equation:
σ=D·∈
(3) Soil mass vibration propagation equation:
(4) A soil deformation coordination equation:
(5) Pile-soil interaction equation:
p=C1·Es·u+C2·σ′v·tanφ·u
these equations together describe the behavior of the pile foundation-soil dynamics system during pile foundation construction.
According to step S60, the above equation set is solved to obtain 5 analytical solutions, which respectively describe the vibration propagation characteristics, stress distribution characteristics, deformation characteristics, pile-soil interaction characteristics and pile foundation bearing capacity characteristics of the soil body. Taking the analysis solution of soil stress distribution as an example:
σ(x,t)=B exp(-αx)sin(ωt-kx+φ)
Wherein B is stress amplitude, alpha is attenuation coefficient, and phi is phase. The analysis solution reflects the change rule of soil stress along with space and time.
5. Load bearing assessment
Based on the dynamics analysis model established in the step S70, the characteristic parameter set X obtained by on-site monitoring is used as input, and the stress-strain distribution sigma (X, t) and epsilon (X, t) of the soil body around the pile foundation are obtained by solving an equation set through a numerical value.
It can be seen from the figure that during pile foundation construction, the soil stress and strain do have large space-time variation. This non-uniform stress-strain distribution necessarily affects the side and end drag of the pile foundation.
According to step S80, the side friction resistance Qs and the end resistance Qb of the pile foundation are calculated by using the soil stress-strain state. The result shows that under the action of soil squeezing effect, the shear strength parameters c and phi of soil near the bottom of the pile foundation are obviously reduced, and the side friction resistance Qs is reduced by about 12%. Meanwhile, the stress concentration of the soil body at the end part of the pile foundation is weakened, and the end resistance Qb is reduced by about 8%.
Comprehensive calculation shows that the total bearing capacity Qb of the engineering pile foundation is reduced by about 10% under the action of soil squeezing effect, namely the bearing capacity change index eta= -10%.
According to step S90, this magnitude of load bearing capacity reduction is considered to have exceeded an acceptable range, and reinforcement measures are required. Meanwhile, as can be seen from a soil stress-strain distribution diagram, soil strain near the bottom of the pile foundation is large, and the soil strain is a main cause area for bearing capacity reduction and needs to be focused.
Aiming at the analysis results, the following reinforcement measures are proposed:
(1) The number of pile foundations is properly increased, and the overall bearing capacity is improved;
(2) The reinforcement measures such as micro piles or soil nails are additionally arranged near the bottom of the pile foundation, so that the local soil intensity is improved;
(3) And the bearing capacity of the single pile is improved by adopting high-strength concrete or a prestressing technology.
By implementing the reinforcement measures, the total bearing capacity of the pile foundation can be expected to be restored to the original design level, and the safety and reliability of the engineering structure are ensured.
6. Summary
By adopting the pile sinking soil compaction effect evaluation method based on vibration-strain signal analysis, the pile foundation bearing capacity change condition of the engineering is comprehensively evaluated. The result shows that in the pile foundation construction process, the vibration and deformation response of the surrounding soil body are indeed changed greatly, so that the bearing capacity of the pile foundation is obviously reduced.
Compared with the existing empirical analysis method, the method fully utilizes field monitoring data, and can more accurately describe and predict the dynamic behavior of the pile foundation and the soil body by combining advanced signal processing and dynamic analysis technology. And by quantitatively calculating the load capacity change index and analyzing the potential reduction area, a more scientific technical basis is provided for engineering personnel, and targeted reinforcement measures are facilitated.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention.